"We have come! We are death!"
- – These guys have one of the best battle cries in the franchise.
The most feared branch of the Hexagrammaton, the Dreadwing was called in when the total annihilation of the enemy was necessary. Its members were masters of massacres, purges, and the deployment of Exterminatus-class weaponry. They also specialized in using terror as a weapon. Far from dumb brutes, it fell to the initiates of the Dreadwing the caretaking and maintenance of some of the most dangerous technologies to exist within the Imperium, they were the First Legion's "dirty tricks department", with all sorts of secret and very nasty gear that they really shouldn't have - really shocking stuff, like radioactive plasma weapons, vortex artillery, and phosphex flamethrowers. Seeing as how the First Legion was... well, the first Space Marine Legion, and had fought in the Terran Unification wars, they likely had far more access to all the horrifically destructive weaponry that is now kept under lock and key deep within the Imperial Palace.
The Dreadwing was an amalgamation of the earlier Host of Bone, maintaining many of its Scandinavian ceremonies and titles despite the influx of recruits from Caliban, along with the Host of Stone, renowned for their expertise in defense and siege warfare.
Its members were known to be grim but capable of safely operating some of the most dangerous technologies in the Imperium. Its ranks included most of the Legion's Destroyer Squads and Interemptors but also a large number of Techmarines and Apothecaries. In its sealed vaults rested the least stable Legion Dreadnoughts, those whose minds had eroded to the point of savageness.
When despair and loss forced the ideals of the Great Crusade to be rejected, the Dreadwing became the host for those warriors who were allowed to use their psychic powers by the primarch.
There is a nonzero chance that they became the Star Phantoms following the implementation of the Codex.
Due to the nature of their weapons, i.e. gives you cancer that impairs Space Marines. The Dreadwing would most likely had the highest amount of Astartes with cybernetics near or on par with the Iron Warriors and below the Iron Hands.
- Farith Redloss - Voted-Lieutenant of the Dreadwing (takes out a World Eaters Leviathan Dreadnaught with his axe). Was sent a message by the Watchers to get the Dark Angels to return to Caliban before it was too late, but gave up arguing when weighed against his loyalties to the Lion and his friendship with Holguin.
- Farith Redloss would survive the Horus Heresy and the Fall of Caliban, and go on to become the first commander of the Dark Angels chapter following the Second Founding, as well as the first interrogator of Luther, and he was there when Cypher presented himself at the Rock and informed the gathered Masters of the existence of The Fallen. Redloss died almost three decades before the War of the Beast.
- Marduk Sedras - one of the oldest members of the Astartes, being 250 years old by the time of the Horus Heresy. Decided that command wasn't for him, so passed up the job of Master so he could stay on the front lines. Has a massive blade called the Death of Worlds, composed of fragments of adamantine from each world he has participated in the destruction of. Needless to say that the sword is now so large and heavy that only the strongest members of the Legion are able to actually carry it!
The Dreadwing are represented on the tabletop by the Dreadwing Interemptor, a unique unit of Dark Angels that are essentially what you get if you took a Destroyer Squad and decided to give them rapid-fire plasma weapons.
Even among the ranks of the Dreadwing the Interemptors were known as a grim breed dedicated to the singular purpose of utterly annihilating the enemy. When they attacked, they left behind no trace of their foe and took no trophies or told no tales of their victories. They were considered the Lion's ultimate sanction.
Interemptors wielded Plasma Burners, Rad Missile Launchers that could also be equipped with Stasis Missiles, Plasma Incinerators, Chainswords, Phosphex Grenades, Krak Grenades, and Rad Grenades. Their radioactive weaponry was devastating but degraded the warriors over time as the Mark III: Iron Armour doesn't provide modern protection against intense radiation poisoning. Thus a Dreadwing Interemptor was only combat-viable for a few decades before requiring bionic augmentation or entombment within a Dreadnought.
Other Unique Units
They also had a Terminator unit called the Naufragia; Terminators armed with Phosphex Incinerator Cannons and ye old Plasma weaponry, though they have not been seen on the tabletop. Since the Dark Angels can already field five different types of Terminators in the same army. You can see why they didn't. Although Naufragia would be right out superior to Nullificators based on weapons alone. So Dark Angels would have no use for the latter in fluff or crunch.